Polymerization product and process for molding same



Patented June 30, 1936 UNITED STATES PATENT OFFICE POLYMERIZATIONPRODUCT PROCESS FOR MOLDING SAME No Drawing. Application August 8, 1934,Serial No. 738,930

7 Claims.

This invention relates to a new polymerization product and a process formolding same and, more particularly, to polymerized methyl alphamethacrylate in solid form but containing innumerable small cavities,and to a process of preparing this form of polymerized methyl alphamethacrylate and molding same. This application is a continuation inpart of applicants copending application Serial No. 641,113, filedNovember 3, 1932, entitled Resin and resin-forming compound.

An object of the present invention is to provide a. simple andeconomical process of preparing molded articles comprising methyl alphamethacrylate. A further object is to provide a process wherein methylalpha methacrylate polymer compositions may be'employed in thecomminuted form that heretofore known molding compoundshave been used inthe manufacture of molded articles. A still further object is to providea commercially feasible process wherein the polymerization of methylalpha methacrylate may be accomplished without careful control and yet aproduct be obtained having properties highly favorable for themanufacture of comminuted molding compounds. Other objects of theinvention will be apparent from the description given hereinafter.

The above objects are accomplished according to the present invention bypolymerizing monomeric methyl alpha methacrylate under conditions suchas to give a solid mass full of small cavities, comminuting said mass,and molding said comminuted mass, either with or without pelleting,under heat and pressure.

Monomeric methyl alpha methacrylate may be obtained by treating methylalpha hydroxyisobutyrate with a dehydrating agent, e. g. phosphoruspentoxide. Methyl alpha methacrylate is a water white liquid, boilingpoint -101 C.

at atmospheric pressure, freezing point about 56 C., specific gravity0.94 at 20 C. It may be polymerized, according to this invention, bymeans of heat, light, and/or catalysts, e. g., as described for thepolymerization of organic vinyl esters in British Specification No.15,271/1914. Preferably a catalyst such as oxygen, ozone, organicperoxide, and ozonide, or an agent giving off oxy en, is employed. Thepolymerization is effected in the absence of solvent or diluent, or inthe presence of a. negligible amount of either.

The polymerization of monomeric methyl alpha methacrylate is preferablycarried out at an elevated temperature such as 60-100 0., or even at ahigher temperature, such as C. The polymerization reaction is stronglyexothermic and, in order to obtain a clear,.solid polymerized mass freeof flaws or other internal defects, it is necessary to carefully controlthe conditions under which the polymerization takes place. Particularlyis it necessary to carefully maintain a temperature control so that theexothermic heat of reaction does not greatly increase the temperature ofthe mass being polymerized. Where the monomer is being polymerized inrelatively large bulk, as contrasted to minute quantities or largerquantities in thin films, the most careful control of the temperature isrequired to give a mass free of internal flaws.

While it. is quite feasible to produce molded articles free of internalflaws by polymerizing the monomer directly in molds, the conditionsunder which the polymerization is carried out must be carefullycontrolled and the time of polymerization is relatively long.Accordingly, the production of molded articles in this manner is fairlyexpensive. According to the present invention, a great economy iseffected by carrying out the polymerization of the monomer at a veryrapid rate at relatively high temperatures and without any attempt attemperature control. When this is done with a relatively large bulk ofthe monomer, it inevitably results in a solid mass more or less opaqueand full of small cavities. Presumably such cavities are caused byvolatilization of the monomer, or possibly through substances in themass such as occluded air, or auxiliary ingredients of high volatility.The volatilized substance as a gas may pass up through the bulk ofmaterial at the commencement of the polymerization but after theviscosity of the material increases as polymerization progresses it isno longer possible for this volatilized material to escape and henceinnumerable small cavities are formed in the material. Dependingsomewhat on specific conditions, the polymerized solid mass may be fullof small bubbles or may be of a more porous or pumice-like character butin all cases the mass is full of small cavities and a characteristic ofthe mass is its friability. The greater the percentage of cavities inthe mass, the greater is this friability so that no advantage is gainedby careful temperature control, and the like, during polymerization.

According to the present invention, advantage is taken of thepolymerized solid mass full of cavities by comminuting same in any wellknown grinding apparatus to give a molding compound. This moldingcompound may be pelleted to put it in more convenient form forintroduction into molds, or may be directly introduced into molds andmolded under heat and pressure.

In order to illustrate the invention, the following examples aregiven:--

Example 1.-Monomeric methyl alpha methacrylate (b. p. 100-101 C.) ismixed with 0.5% by weight of benzoyl peroxide and the mixture is heatedat 100 C. for four hours. On cooling a pumice-like mass is obtained.This is pulverized and, for example, 20 grams is introduced into a discmold, 4 diameter, which is then heated at 140-450 C. for two minutesunder a pressure of 2 tons per square inch. The mold is cooled to belowC. and the molded disc ejected.

The molded disc is hard, tough, transparent, colorless, and free frombubbles. It has taken the shape of the mold perfectly. The moldedsubstance does not soften at temperatures of (SO- C. and does notbecomes brittle at 0 C. It is highly resilient and possesses a highshock resistance. It does not absorb moisture.

As an alternative procedure and for the purpose of facilitating themolding operation the powdered polymer, prior to introduction into themold, may be mixed with one-third its weight of butyl phthalate.

Example 2.-Four parts by weight of monomeric methyl alpha methacrylateand 1 part of dibutylphthalate are mixed and 0.04 parts of benzoylperoxide are added. Polymerization is carried out as described inExample 1. The mass obtained is pulverized and molded at -100 C. and 1ton per square inchpressure. The molded substance resembles that ofExample 1, but softens at a somewhat lower temperature. It has a highshock resistance, somewhat lower than that of the product of Example 1.

Example 3.--To 100 parts of monomeric methyl alpha methacrylate areadded 0.3 parts of sodium perborate and 0.65 parts of acetic anhydride.The mixture is then heated at 60 C. Polymerization sets in after 4hours, and proceeds smoothly, the mass becoming more and more viscous,until after 20 hours, polymerization appears to be substantiallycomplete.

The polymer so obtained is a hard, tough, perfectly colorless mass,transparent but filled with bubbles. The mass is pulverized ready foruse in molding. An illustrative example of this will be given.

Twenty grams of the pulverized polymer are introduced into a 4" diameterpositive mold and subjected to a pressure of 8 tons per square inch at125 C. for 2 minutes. The mold is then cooled to C. and the molded discejected.

Example 4.Thirty parts of monomeric methyl alpha methacrylate and 0.15parts of benzoyl peroxide are mixed and 10 parts of titanium white and10 parts of china clay are added to give a suspension. This is heated atC. for 4 hours. The pigmented polymer is pulverized, and can then bemolded into white opaque bodies which are light fast and possess goodmechanical properties.

Example 5.--One hundred parts of monomeric methyl alpha methacrylate aremixed with 0.5 parts of benzoyl peroxide and 0.1 parts of the diazodyestuff obtained by coupling tetrazotizeddiamino-di-pxyl01phenylmethane with B-naphthol. The dyestufi dissolves.The mixture is heated for 4 hours at 100 C. The so obtained polymergives beautiful, transparent bright orange red molded bodies.

.It will be understood that the above examples are merely illustrativeand the invention broadly comprises polymerizing a. composition chieflycomposed of monomeric methyl alpha methacrylate under conditions such asto give a solidified mass full of small cavities and then comminutingsaid mass to granular form to give a molding compound which may bemolded under heat and pressure into any desired shape.

There are numerous methods of polymerizing the monomer to get asolidified mass full of small cavities. Primarily these small cavitiesare caused by heat volatilizing some constituent of the mass beingpolymerized, although the rapidity of polymerization also seems to causethese cavities due, it is believed, not only to the exothermic heatgenerated during the reaction but also to the fact that occluded airand/or other gases are not freed from the mass until polymerization hasprogressed to a state where the mass is too viscous to permit escape ofthe gases.

Conditions that will give a maximum of small cavities, bubbles, pores,or the like, in the solidifled mass are preferably maintained duringpolymerization because the resulting mass is thereby more readilycomminuted and, further, it is easier to maintain such conditions andpolymerization is efiected in a shorter period. For this reason, thepolymerization is carried out at elevated temperatures, preferablyheating the mass to be polymerized to around 100 C. This accelerates thepolymerization reaction and causes formation of gases giving, as an endproduct, a solidified mass full of small cavities. Heating to highertemperatures may be employed but in so 2 doing volatilization of themonomer or auxiliary ingredients in the composition to be polymerizedmay take place to such an extent as to be uneconomical. Heating to atemperature as low as 60 C. may also be used successfully if theexothermic heat of reaction is not permitted to escape at the rate ofits formation.

It is preferred to carry out the polymerization, according to thepresent invention, on relatively large bulks of the monomeric methylalpha methacrylate as compared to polymerizing minute quantities orlarger quantities in thin films. The reason for this is that, where themonomer is being polymerized in a relatively large bulk, obviously theexothermic heat of reaction cannot escape so readily and, as a result,the temperature inside the mass being polymerized quickly rises to apoint where gases are being formed. It is for this reason that, evenwhen the monomer is only heated to a temperature of 60 C., gases areformed within the material and, consequently, a solidified mass full ofcavities is obtained. A further reason for polymerizing the monomer inbulk form rather than in thin films is that the distance a bubble of gasmust travel through the material being polymerized in bulk form toescape from the mass is far greater than the distance the bubble musttravel to escape where polymerization is carried out in thin films. V

The selection of a catalyst, where it is desired to employ a catalyst,having great activity and the use of a relatively large amount of thecatalyst, both tend to further increase the percent of small cavities inthe material being polymerized since the accelerating of thepolymerization reaction results in the generation of exothermic heat ata rate far in excess of that at which it is withdrawn form the mass.

' clohexyl, methyl cyclohexyl According to this invention, variousauxiliary agents may be added to the monomerlcmethyl alpha methacrylateeither before polymerization or to the polymerized product in comminutedform. Among such materials may be mentioned filling materals, e. g.china clay, wood flour, asbestos, and the like, and coloring matters,both soluble and insoluble. Likewise, effect materials of the type ofmetallic powders and crushed mica may also be added.

Plasticizers maybe added to the methyl alpha methacrylate compositionseither prior to polymerization or subsequently thereto, as illustratedin the examples. The particular plasticizer selected and the quantitythereof employed will, of course, be dependent upon the particular usefor which the composition is intended, as will be understood by thoseskilled in the art. Among plasticizers suitable for use in accordancewith the present invention may be mentioned: camphor; phthalates, suchas ethyl, propyl, isopropyl, butyl, isobutyl, cyclohexyl, methylcyclohexyl, or benzyl phthal'ate or phthalates of the mixed type such ascyclohexyl butyl, benzyl butyl or butyl lauryl pl'ithalate; esters ofdibasic acids, such as the ethyl, propyl, isopropyl, butyl, isobutyl,cy-

or benzyl esters of succinic, fumaric, tartaric, adipic and sebacicacids; esters of monobasic acids, such as the butyl, isobutyl,cyclohexyl, methyl cyclohexyl, benzyl or lauryl esters of lauric,laevulinic, benzoic, benzoyl propionic and benzoyl benzoic acids; estersof polyhydric alcohols, e. g. glycol and glycerol, such as glycolbenzoate, glycol laevulinate, triacetin, tripropionin and tributyrin;substituted toluene sulphonamides, such as ethylparatoluenesulphonamide; substituted amides, such as tetraethylphthalamide, tetrabutyl succinamide, tetrabutyl adipamide; hydrocarbons,such as dixylyl ethane; halogented hydrocarbons, such as chlorinateddiphenyls and dichlordibenzyl; other compounds such as dicresoxy ethylether; and non-drying or semi-drying oils,

such as castor oil.

The solified polymerized methyl alpha methacrylate full of smallcavities may be readily comminuted to granular form in any well knowngrinding apparatus such as a three-roll mill, or the like. If desired,this granular material may be formed into pellets which are subsequentlyintroduced into molds for molding articles. This is well known moldingshop practice and is optional. Despite the fact that the solified massis full of small cavities, the bulk density of the material in granularform is entirely satisfactory for use in the standard molding shopequipment. Those skilled in the art will understand that by the termbulk density is meant the weight of the material per unit volume,materials of very low bulk density being extremely awkward to employ inthe standard molding shop equipment.

The conditions under which the molding com.- pound herein underconsideration may be molded, can be varied widely. It is preferred thata temperature of at least 80 C. be employed for molding and, quitecommonly, temperatures well above 100 C. are employed for this purpose,the most satisfactory temperature being somewhat dependent upon whethera plasticizer is employed and also the amount and activity of suchplasticizer. Temperatures ranging anywhere from 80-200 C. may besuitably employed. The pressure may range from 0.1 to as high as 8 tonsper square inch. Under certain circumstances, the use of anexceptionally high pressure in the neighborhood of 8 tons per squareinch is advantageous where the molding apparatus employed is of heavyenough construction to stand such pressure. It is preferable that themold be cooled to below 100 C. before the molded body is removed.

Molded products according to the present in- I vention are surprisinglytough, hard, and rigid and generally possess a high mechanical strengthwhich remains substantially unaffected by changes in atmospherictemperature. When the polymerization product is used alone, the moldedbodies are colorless and light fast and possess a glass-liketransparency. They remain practically unaffected by immersion for longperiods in water. In electrical properties such as volume resistivity,phase angle difference, and freedom from tracking, these molded productsare superior to those made from well known phenol-aidehyde compositionswhich find such a wide application in the electrical industry. Theseproducts are relatively uninflammable, tasteless and odoress.

The present invention is applicable for the preparation of moldedproducts of all kinds and descriptions. It may be employed for theproduction of finished articles or for the production of intermediateshapes which are subsequently machined, ground, polished, or the like,to give a finished article. Likewise, the comminuted polymerized massmay be molded in the form of slabs, discs, sheets, or the like, forvarious uses such as interlayers in unsplinterable glass, and the like.Molded articles such as tableware, knick-knacks, novelty cases,cabinets, and the like, are readily made according to the presentinvention. By suitably choosing soluble dyestuffs and by stratifying, orotherwise filling the mold, variegated effects of remarkable beauty maybe obtained.

An advantage of the present invention is that Q it provides such aneconomical and easily carried out process for making molded articles.Whereas methyl alpha methacrylate may be polymerized in a mold to give afinished article, the conditions under which this polymerization must becarried out to give an article free of internal visual flaws must becarefully controlled and the polymerization prolonged for an appreciableperiod. On the other hand, according to the present process, thepolymerization may be carried out as rapidly as possible with littlecontrol of temperature or other conditions and yet the resulting productis much better suited for comminuting and use as a molding compound thanwould be the product of extremely careful polymerization having no smallcavities or flaws whatsoever. A further and unexpected advantage of thepresent invention is that it gives a molding compound of verysatisfactory bulk density, despite the fact that the polymerized massbefore comminuting is filled with small cavities.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. Process of preparing a moldable composition comprising heating arelatively large bulk of monomeric methyl alpha methacrylate to initiatepolymerization and allowing said polymerizthermic heat of reaction buildup in the mass until fa solidified mass full of small cavities isIormed.

2. Process of preparing a molding compound comprising heating arelatively large bull: of monomeric methyl alpha methaorylate toinitiate polymerization, allowing said polymerizing action to proceedrapidly by having the exothermic heat ofreaction build up in the massuntil a solidified mass full of small cavities is formed, andcomminuting said mass to granular form.

3. Process of preparing a molding compound comprising heating a.composition chiefly composed of monomeric methyl alpha methacrylate to atemperature above 0., allowing the resulting polymerization action toproceed rapidly by having the exothermic heat of reaction build up inthe mass until said methyl alpha methacrylate is polymerized to asolidified mass full of small cavities, and comminuting said mass togranular form.

4. Process of preparing a molding compound comprising heating arelatively large bulk of monomeric methyl alpha methacrylate to about100 C. until said methyl alpha methacrylate is polymerized to asolidified mass full of small cavities, and comminuting said mass togranular i'orm.

cavities, comminuting said mass, and molding said comminuted mass underheat and pressure.

6. Process of preparing molded articles com- 10 prising heating arelatively large bulk of monomeric methyl alpha methacrylate to about100 C. until said methyl alpha methacrylate is polymerized to asolidified mass full or small cavities, 5

and molding said comcomminuting said mass, minuted mass under heat andpressure.

'7. Process of preparing molded articles comprising heating a relativelylarge bulk of monomeric methyl alpha methacrylate to about 100 20 C.until said methyl alpha methacrylate is polymerized to a solidified massfull 01' small cavities, comminuting said mass, and molding saidcomminuted mass at a temperature above about C.

and a pressure above 0.1 ton per square inch.

ROWLAND HILL.

